Nowadays ALL carriers advertise 'departure time' as being anything from 10 mins to 45 mins (long haul) longer than they are. You often take off 'late' but amazingly arrive on time after a sector of only 45 minutes.
It's a classic case of:
1) Set target limits that will be published in the press so that people can choose the most punctual carrier.
2) Watch the Marketing departments fix the system so that they are higher up the tables.
I would never choose a carrier solely on whether it is 'punctual' as each rotation is different.